1. Field of the Invention
The present invention relates to a method of and an apparatus for setting color separation rules for use in separating colors of a color image in a color image processor such as a color process scanner.
2. Description of the Prior Art
As well known in the art, a color process is operable to read a color original by reading each pixel thereof in the order of scanning lines, and color image data thus obtained is subjected to color separation processing, to obtain image data for reproducing a color image.
Such color separation is performed in accordance with various color separation rules. An important one out of the rules concerns memory colors included in the color original. The "memory colors" are such colors that humans often observe in their daily life through visual experience and remember the impression thereof.
For example, if the percentage of areas of the memory colors such as a skin color of a human being, a green color of trees and plants, and a blue color of the sky and the sea in the color original is relatively large, the memory colors must be reproduced on a print in a color tone corresponding to the impression on humans in order to render a good-quality print. Therefore, the color separation rule for memory colors must be different from standard rules.
Furthermore, in some cases gradation curves may be shifted relative to normal curves prepared with reference to gray tones. For example, when a skin color of a human being is in the color original, the intermediate density part of a gradation curve is corrected such that the density of ink on a magenta (M) block is slightly higher than those of an yellow (Y) block and a cyan (C) block. Consequently, a gray portion of the original is reproduced at a slightly reddish tone while a skin-colored portion thereof is a reproduced in a color more similar to the color of the skin remembered by humans, resulting in a desirable print.
Such correction processing of memory colors has been conventionally performed manually.
However, since most of color originals whose colors are separated by a color scanner include such memory colors, the above-indicated correction for the memory colors is frequently required. Therefore, there is a problem of significantly increasing the burden on the operator.
Additionally, considerable experience for manual operation of a color scanner is required in such setting of the color separation rules for the memory colors. Thus, there are problems of the difficulty in standardizing the manual work and in variations in quality of prints depending on the subjectivity of the operator.
In order to deal with these problems, it is desired to automate setting of the color separation rule with respect to memory colors. However, as techniques for automatically setting the color separation rule in the color scanner, only a technique for automatically setting the color separation rule with respect to a gray tone has been known. Techniques suitable for automatically setting the color separation rule such as a gradation correction rule and a color correction rule has not been actually developed.